Surface treatment of magnetic recording heads

ABSTRACT

Surface modification of magnetic recording heads using plasma immersion ion implantation and deposition is disclosed. This method may be carried out using a vacuum arc deposition system with a metallic or carbon cathode. By operating a plasma gun in a long-pulse mode and biasing the substrate holder with short pulses of a high negative voltage, direct ion implantation, recoil implantation, and surface deposition are combined to modify the near-surface regions of the head or substrate in processing times which may be less than 5 min. The modified regions are atomically mixed into the substrate. This surface modification improves the surface smoothness and hardness and enhances the tribological characteristics under conditions of contact-start-stop and continuous sliding. These results are obtained while maintaining original tolerances.

This invention was made with government support under Grant Nos.MSS-8996309 and DE-AC03-76SF-00098 awarded by the National ScienceFoundation and the U.S. Department of Energy. The Government has certainrights in this invention.

This is a continuation of application Ser. No. 08/472,939, abandonedfiled Jun. 6, 1995, which is a divisional of 08/306,750, now U.S. Pat.No. 5,476,691, filed Sep. 15, 1994, which is a continuation of08/185,608, filed Jan. 21, 1994, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates generally to surface treatment ofceramics, and more particularly to a surface treatment for magneticrecording heads using plasma immersion ion implantation and deposition.

The use and development of plasma- and ion-assisted materialmodification processes to selectively alter the structure andphysicochemical properties of surfaces has received increasing attentionin recent years. In particular, ion implantation as a nonequilibriumprocess provides a unique means for developing surface layers with novelcompositions and microstructures that are otherwise difficult orimpossible to obtain. In conventional ion implantation, a beam ofenergetic ions extracted from a plasma source is accelerated toward thesurface to be implanted. The ions impinging on the solid surface at highenergy become buried at depths typically in the range of 0.01 to 1microns (μm), thus resulting in the modification of the atomiccomposition and lattice structure of the near-surface region withoutaffecting the surface roughness, dimensional tolerances, and bulkmaterial properties, as in the case of other high-temperature vacuumcoating techniques. Metallurgical reactions that occur with ionimplantation, such as a solid solution of implant element, generation ofdislocations and point defects, alteration of crystallinity(amorphization), precipitation of second phases and compound formation,and changes in the chemical composition and stress-strain state, canproduce a significant hardening and strengthening effect on a thinsurface layer which, in turn, may greatly enhance the fatigue life,oxidation resistance, and tribological properties, such as friction andwear, of a wide range of base materials used in various industrial andmedical prostheses applications.

Since ion implantation is a line-of-sight operation, componentmanipulation and beam rastering are required in order to achieve spatialuniformity in treatment. This limits the size of the component that canbe implanted (target) and imposes a need for special fixturing.Furthermore, the necessity to provide sufficient heat sinks and maskingto inhibit excessive heating and sputtering of the target introducesadditional complexity to the process. Plasma source ion implantation isa non-line-of-sight implantation technique of greater processingthroughput which circumvents the aforementioned drawbacks andrestrictions. The target is immersed in a plasma and repetitivelypulse-biased to a high negative voltage relative to the plasmapotential. A plasma sheath forms around the target and the ionsaccelerate through the electric field of the sheath bombarding allexposed areas of the target simultaneously. Although this processprovides an effective means for achieving enhanced surface properties,it is limited to implanting species that are gaseous at roomtemperature, e.g., nitrogen and oxygen.

It is apparent from the foregoing that unique surface properties can beobtained with the plasma immersion ion implantation technique. One ofthe most rapidly emerging technologies where significant advancements inmaterials processing can be achieved with such a technique is magneticrecording media. As magnetic hard disk drives have evolved to higherstorage densities, the head-disk spacing (flying height) has beenreduced to the present state-of-the-art of -0.1 μm. Remarkably smallerspacings, in the range of 0.025 to 0.05 μm, are predicted for the nearfuture in view of the technology trend for much higher storagedensities. Operation at such low flying heights enhances theintermittent contact of the magnetic recording head with the disk, thusresulting in friction build-up and accelerated wear damage of both headand disk surfaces. Although significant progress has been made towardthe development of durable thin films for hard disks, surfacemodification of magnetic recording heads, or other ceramic articles, forenhancing the friction and wear characteristics at the head-diskinterface has received relatively less attention.

Accordingly, an object of the present invention is to provide a methodfor improving the friction and wear properties of magnetic recordingheads and other ceramic articles.

Another object of the present invention is to provide a method forenhancing the smoothness and hardness of magnetic recording heads andother ceramic articles.

Yet another object of the present invention is to provide a lowtemperature and short duration surface treatment for enhancing thesmoothness, hardness, friction and wear properties of magnetic recordingheads and other ceramic articles.

Still another object of the present invention is to provide a surfacetreatment for magnetic recording heads and other ceramic articles thatcan be carried out using a wide variety of solid metal, solid nonmetaland gaseous species.

A further object of the present invention is to provide a surfacetreatment for magnetic recording heads and other ceramic articles,yielding a combination of phases attainable by deposition and phasesattainable by ion implantation with atomic interfacial mixing.

Another object of the present invention is to provide a surfacetreatment for magnetic recording heads and other ceramic articleswherein original tolerances are maintained.

Still another object of the present invention is to provide a surfacetreatment for modifying the surface resistivity of magnetic recordingheads and other ceramic articles.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theclaims.

SUMMARY OF THE INVENTION

The present invention is directed to a surface treatment for magneticrecording heads and other ceramic articles or substrates. A ceramicsubstrate, for example, may be held on a conductive substrate holder andenclosed in a low pressure ambient in a hermetic enclosure and immersedin a plasma comprising ions of a solid material. At the surface of thesubstrate, the plasma density may be in the range of about 10⁶ to 10¹³ions per cubic centimeter (cm⁻³). In the case of electrical conductors,such as metals, carbon and highly doped semiconductors, the plasma canbe generated using a vacuum arc. A plasma containing these materials orinsulators can also be generated by laser ablation. Any method can beused to generate this plasma as long as the substrate is not impacted byany macroparticles that are produced along with the plasma. Part of thetime that the substrate is immersed in the plasma, the substrate holderis kept at a low potential close to the plasma potential such thatmaterial from the plasma condenses onto the surface of the substrate. Atother times, the substrate holder is kept at a negative bias relative tothe plasma such that ions from the plasma are accelerated and implantedinto the substrate. This negative bias may be in the range of about 20 Vto 100 kV, and may be pulsed with a duty cycle of at least about 1%. Thetotal dose of ions impinging on the substrate may be in the range ofabout 10¹⁴ to 10¹⁸ ions per square centimeter (cm⁻²).

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, schematically illustrate a preferredembodiment of the invention and, together with the general descriptiongiven above and the detailed description of the preferred embodimentgiven below, serve to explain the principles of the invention.

FIG. 1 is an enlarged schematic illustration of a plasma gun andmagnetic filter for the practice of the present invention.

FIG. 2 is a simplified diagrammatic illustration of a surface treatmentapparatus for the practice of the present invention.

FIG. 3A is a timing diagram of a processing cycle.

FIGS. 3B-3H are simplified diagrammatic illustrations of a multi-layerstructure according to the present invention.

FIGS. 4A-4C are simulated depth profiles of surfaces of magneticrecording heads treated according to the present invention.

FIG. 5 is a velocity versus time profile for contact start stop (CSS)tests.

FIGS. 6A-6D show measured coefficient of friction and touchdown velocity(TDV) versus the number of CSS cycles.

FIGS. 7A-7D show the evolution of the coefficient of friction with thenumber of sliding revolutions.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be described in terms of the preferredembodiment. The preferred embodiment is a surface treatment process forceramic substrates such as magnetic recording heads and the articles sotreated.

The treatment of the present invention requires that the substrates beimmersed in a plasma comprising ions of a solid material. Such a plasmamay be produced by laser ablation or, in the case of conductivematerials, by a vacuum arc plasma gun.

As shown in FIG. 1, a plasma gun 28 comprises a cathode rod or disk 10in the central part of the gun, surrounded by a ceramic insulator 12 anda cylindrical anode 14. The arc pulses are initiated by a short (oforder 10 microseconds) high voltage (for example 15 kilovolts) triggerspark between cathode 10 and a trigger electrode 16. A magnetic field isprovided across anode chamber 21 by a solenoid 20. The plasma is createdon the cathode surface and leaves the source through aperture 23 ofchamber 21.

Cathodic arcs are characterized by plasma production at micron-size,non-stationary cathode spots. Their "pure" occurrence can be observed asvacuum arcs; i.e., when no gas is present between the electrodes, andthus the plasma carrying the arc current is exclusively produced in thecathode spots. The cathode material undergoes a complicated transitionfrom the solid to a plasma, and this transition is different fromevaporation or sputtering since little neutral cathode vapor isinvolved. The principal cathode spot mechanisms remain the same if a gasis present and if the cathode temperature is relatively low. From thispoint of view, "cathodic arcs" include a broader class of dischargesthan "vacuum arcs".

The pressure within the cathode spots is extremely high (up to 10¹⁰Pascal (Pa)=10⁵ bar), and the dense plasma rapidly expands into thevacuum or low-pressure gas ambient driven by the intense pressuregradient. Ions are accelerated by the combined forces of the pressuregradient, local electric fields, and electron-ion friction. It has beenfound that the final ion velocity for all cathode materials is about1-2×10⁴ meters per second (m/s), corresponding to ion energies of 20-200electron volts (eV) depending on the ion mass.

The use of cathodic arc plasmas implies a directed flow of plasma, andtherefore one typical feature of "conventional" gaseous plasma sourceion implantation, namely implanting simultaneously into all sides of thesubstrate, is lost. The picture is similar to ion beam implantation: thesurface facing the plasma flow is treated while the side and downstreamsurfaces remain nearly unchanged. Plasma source or substrate motion isnecessary if an all-side treatment is required, or several sources mustbe used simultaneously or sequentially.

Cathodic arcs can be produced in the broad range between submicrosecondsand d.c. operation. It is often convenient to use a pulse formingnetwork or even just a simple capacitor and load resistor (of order 1 Ω)to obtain repetitive arc discharges of, for instance, 100 microseconds(μs)--1 second duration.

Plasma source ion implantation with a metal (and carbon) plasma resultsin surface modifications qualitatively different from those obtainedwith a gaseous plasma. Since direct ion implantation and recoil ionimplantation occur concomitantly during the high-voltage bias pulses(implantation phase) and the metal plasma condenses and remains on thesurface as a film between the bias pulse (deposition phase), thissurface modification process is referred to as metal plasma immersionion implantation and deposition. Thus, a wide range of materialmodifications can be obtained by adjusting the implantation/depositionduty cycle and the magnitude of the substrate holder bias voltage, whilewith the optional use of reactive gases compound films can be alsoproduced. Of particular significance is the increased solid solubilitiesof condensable species obtained from recoil collision cascades and theinterface tailoring on an atomic scale resulting from the mixing of thefilm and substrate materials. Intermixing greatly enhances the filmadhesion and reduces stresses due to lattice mismatches.

Cathodic arc plasma sources for thin film formation can be operatedeither in a repetitively pulsed mode with an arc pulse duration between50 μs and hundreds of milliseconds or d.c. The arc current may be in therange of 5-2000 amperes (A) and is typically in the range of 100-250 A.Guns operated with short pulses and moderate repetition rates (up to 5pulses per second) do not require cooling if thin films of thicknessbetween monolayers and 50 nanometers (nm) are deposited. For films ofmedium thickness (10-500 nm), arc pulses of up to 5 ms duration at arepetition rate of a few pulses per second can be used. For thick films(100 nm to many microns), water-cooled plasma guns can be operated in along-pulse or d.c. mode of operation. Here the average power becomessubstantial, and substrate cooling is required. Arc repetition rates forthe practice of the present invention may be in the range of 0.1-100pulses per second and more preferably in the range of 0.5-10 pulses persecond.

All metals, alloys, highly-doped semiconductors, and carbon can be usedas cathode material. Thus, cathodic arc deposition can be used for abroad range of thin film structures. Particularly attractive in thecontext of the present invention are silver (Ag), carbon (C), titanium(Ti), gold (Au), platinum (Pt), copper (Cu), tungsten (W), tantalum(Ta), molybdenum (Mo), aluminum (Al), hafnium (Hf) and silicon (Si). Therange of films can be considerably extended by operating in a reactivegas ("reactive deposition"). Metal ions from the cathodic arc plasmasource react in transit to the substrate or at the substrate surfaceforming compound films. The base pressure of the vacuum system may beabout 10⁻⁶ Torr; and the pressure of the working gas may in the range of1-500 mTorr when compound films are deposited.

It is an inherent feature of the cathode spot that not only plasma isformed from the cathode material but also liquid droplets (solidparticles in the case of carbon). These droplets are of size up to 10μm; they are often called "macroparticles" to emphasize their massivenature compared to plasma particles. Macroparticles are mostly largerthan the thickness of the films to be deposited, and film quality can bevery poor if a cathodic arc plasma is used without special "cleaning"measures.

A method for separating plasma and macroparticles is to use a curvedmagnetic field. The underlying idea of filtering is that themacroparticles travel in nearly straight lines due to their inertiawhile the plasma can be guided to a substrate location which is out ofline-of-sight to the cathode spot. Electrons are magnetized (the radiusof their trajectory is much smaller than the duct minor radius, and theyperform many cycles before suffering a collision), and thus they followthe magnetic field lines. Ions are bound to the electron motion byplasma-internal electric fields, and consequently the plasma as a wholefollows the magnetic field lines.

Filtering works only in vacuum and gases at very low pressure since onenecessary condition of electron magnetization is that the electroncollision frequency is much smaller than the electron cyclotronfrequency. At very high pressures, plasma-gas interaction becomesdominant and the cathodic plasma loses its jet-like character which isessential for the plasma transport through magnetic filters.

For macroparticle filtering, a magnetic duct 30 of suitable size is usedso that the plasma streams directly from anode chamber 21 of plasma gun28 into the magnetic duct (see FIGS. 1 and 2). The magnetic field isprovided by solenoids 18. A bent tube 22, such as bellows, and solenoidsform the filter. The solenoids could be replaced by a system ofpermanent magnets. The efficiency of plasma transport can be enhanced byusing a conductive tube wall with positive bias. With optimum magneticfield configuration and optimum bias of the filter wall, about 25% ofthe ions produced in the arc discharge can be transported through thefilter. The magnetic field of the filter may make it difficult totrigger the pulsed vacuum arc. This difficulty may be overcome byconnecting filter solenoids 18 in series with the plasma gun, such thatthe magnetic field is on only after the arc has been triggered. Thefilter wall 22 preferably has a sharp ribbed structure to trap themacroparticles. As shown in FIG. 1, stainless steel welded bellowshaving such a structure may be used for this purpose. A glass tube 24may be inserted in the exit of the bellows to prevent the formation ofanode spots at the sharp duct edges. A substrate 32, such as a magneticrecording head, is held on conductive substrate holder 31 beyond tube 24(see FIG. 2). The deposition rate depends on the plasma density at thesubstrate, which in turn depends on the arc current and on the distanceof the sample or substrate to the filter exit. The plasma density at thesubstrate may be in the range of 10⁶ -10¹³ cm⁻³ and more preferably 10⁸-10¹¹ cm⁻³. The larger the filter exit to substrate distance, the betterthe homogeneity of the film and the lower the deposition rate. Thedistance between the filter exit and the substrate may be as large as 2m, and more preferably 2-50 cm. For example, if the distance betweenfilter and substrate is 10 cm, the area of deposition is ⁻ 10 cm indiameter but only the central part of about 2.5 cm diameter can beconsidered to be homogeneously deposited (deviations of film thickness<10%). The actual deposition rate (during the arc pulse) may be of theorder 10 nm/s, depending on the cathode material, arc current, filterparameters, etc. The average deposition rate is, of course, smaller anddepends on the arc duty cycle. The total dose, which depends on the arcduty cycle and the total process duration, is in the range of 10¹⁴ -10¹⁸cm⁻² and more preferably 10¹⁵ -10¹⁷ cm⁻². For the plasma immersionimplantation phases, the substrate holder may be biased using a highvoltage pulse generator.

As shown in FIG. 2, the surface treatments may be performed in a vacuumvessel 26. Inside vessel 26 are plasma gun 28 and magnetic filter 30.Substrate 32 is positioned on conductive substrate holder 31 at one endof filter 30 beyond tube 24 (see FIG. 1) and plasma gun 28 is situatedat the other end. A pulse generator 36 provides timing signals tosubstrate holder bias pulser 38 and plasma gun pulser 34. As is wellknown in the art, the substrate holder bias pulser may be a high voltagepulse generator that controls the substrate potential, and the plasmagun pulser may be a pulse forming network that powers the plasma gun andthe macroparticle filter solenoids.

The processing cycle is shown schematically in FIG. 3A. The plasma gunpulse duration X is usually much greater than the substrate holder biaspulse period Y such that the substrate holder bias alternates between alow value and a high magnitude negative value while the substrate isexposed to the arc plasma.

Surface modification of ceramic substrates may be accomplished in asequence of two alternating phases, i.e., ion implantation anddeposition in the presence or absence of a substrate holder biasvoltage, respectively. For a certain time period, the substrate 300(FIG. 3B) is subjected to a pulse of a negative potential to acceleratethe positive ions 302 of the plasma across the sheath electric field andimplant them into the substrate 300 (FIG. 3C) forming an ionimplantation layer 303. The pulse may be as short as 100 nanoseconds(ns), and more preferably in the 1-20 microsecond (μs) range. Thepresence of multiply charged ions, which is typical of vacuum arcplasmas, is advantageous since it reduces the required bias voltage fora desired ion energy or implantation depth. The bias voltage may bebetween 20 V and 100 kV and more preferably in the range of 100 V-10 kV.Between the high-voltage bias pulses, the substrate holder is maintainedat near ground potential. In the absence of bias, metal ions arriving atthe substrate surface form a film 304 (FIG. 3D) (their stickingcoefficient is close to one). Ions have a considerable energy even inthe absence of bias, which is associated with their flow velocity.Therefore, they are energetic enough to overcome local potentialbarriers which hinder motion along the surface. Ions move on the surfacesufficiently to be trapped at favorable sites. Metal films produced byfiltered vacuum arc plasmas are therefore denser and smoother than thosefabricated with other deposition methods such as sputtering orevaporation.

In this technique, therefore, surface modification is achieved in acontrolled fashion by means of combining the ion implantation andsurface deposition processes. The substrate holder bias duty cycle maybe as low as 1% and more preferably 5-50%.

As the implantation and deposition phases are alternated, the freshlydeposited film is bombarded with energetic ions. Both direct and recoilimplantation are characteristic of plasma immersion ion implantation anddeposition. At the beginning of the process, an intermixed layer 308 isformed by direct and recoil implantation so the film material 306 mergesgradually into the substrate material (FIG. 3E). Intermixing of film andsubstrate is responsible for the superior adhesion of the resultantfilms formed. Intermixing also reduces the stress associated with thestructural mismatch of substrate and film material. As the film grows(FIGS. 3F-3G), an increasing fraction of ions is implanted not only intothe original substrate but also into the deposited film. When thegrowing film is thicker than the implantation depth (FIG. 3H), ionimplantation does not contribute anymore to intermixing but may beessential to the structure of the film. The ratio of the deposition andimplantation phases is important for the film formation process. Theprocess of the present invention may be carried out starting withcommercially available ceramic heads (sliders). For example, the headsmay be two-rail heads and consist of alumina (Al₂ O₃) and titaniumcarbide (TiC) at weight concentrations of 70% and 30%, respectively, andexhibit a root-mean-square (rms) surface roughness of 2-3 nm. The railsmay be shaped to be approximately 0.5 mm in width and 4 mm in lengthwith leading edges tapered at an angle of 10-15 milliradians (mrad) toenhance the formation of an air bearing during operation.

Ceramic head surfaces were treated with silver, carbon, and titaniumplasmas generated by repetitive vacuum arc discharges using the processof the present invention as described above. Although carbon is not ametal, its graphitic phase can be used as the arc cathode material.Since the condensing hard carbon film contains a high fraction oftetrahedral (sp³) bonding, it may be possible to produce an ultra-thinand hard surface layer consisting of hydrogen-free amorphous diamond, asdemonstrated for silicon substrates.

The substrates may be treated with fixed ion doses of the order of3×10¹⁶ ions/cm², which may be achieved in 5 minutes or less. Longerprocess times are also possible, if desired. The plasma gun is usuallyoperated in a pulsed mode with an arc current of the order of 100 A,pulse duration of the order of 5 ms, and repetition rate of about 2-5pulses per second. For the plasma immersion implantation phases, thesubstrate holder may biased using a high voltage pulse generator. Thebias pulse duration may be 1-20 μs, with a bias duty cycle typicallybetween 10% and 50%. The heads may be placed on a substrate holder whichmay be repetitively biased to a high voltage of -2.0 kV in short pulsesof duration 5 μs and frequency 67 kHz, thus yielding a 30% bias-pulseduty cycle. For these parameters, the implantation dose for the 30% dutycycle, therefore, may be 1×10¹⁶ ions/cm². The duct exit-to-substratedistance may be about 10 cm.

With this surface modification scheme, ion implantation, recoilimplantation, and ion beam mixing occur during one-third of theprocessing time and deposition in the remaining time. For the parametersgiven, the instantaneous deposition rate and the time-averaged rate maybe 2.0 and 0.01 nm/s, respectively. Because the vacuum arc plasma isalmost fully ionized with a mean ion charge state generally between 1⁺and 3⁺, the mean ion energy is greater than the applied voltage by thisfactor. Thus, the mean implantation energy of both silver and titaniumions may be 4.2 keV, while that of carbon ions may be 2.0 keV. For the30% bias-pulse duty cycle, the ion dose between pulses (depositionphase) may be 2×10¹⁶ ions/cm² and the ion energy may be in the range of20 to 100 eV. The plasma density may be on the order of 6×10¹⁰ cm⁻³ andthe plasma flow velocity may be on the order of 10⁴ m/s.

FIGS. 4A-4C show results from simulations revealing the concentration ofimplanted elements as a function of depth from the surface of ceramicrecording heads treated according to the above process parameters. Theshapes of the profiles demonstrate that direct ion implantation, recoilimplantation, and deposition can be accomplished simultaneously with thesurface modification technique of the present invention. The thicknessof the layers modified with silver, carbon, and titanium ions are 13,25, and 18 nm, respectively, as shown in FIGS. 4A, 4B, and 4C,respectively. FIG. 4A shows that the silver-modified layer possesses arelatively uniform composition, except at the surface where theconcentration of implanted silver ions was a little higher. Surfacedeposition in conjunction with ion implantation is mostly apparent inthe elemental depth profiles shown in FIGS. 4B and 4C. The markedlyhigher atomic fractions of carbon and titanium adjacent to the surfacesuggest that the modified heads were also coated with ultra-thin (2-3nm) layers rich in carbon and titanium, respectively. Since thesecompositional modifications change the free energy and shear strength ofthe head surface, significantly different friction and wear propertiescan be obtained.

The effect of the present surface modification technique on the surfacetopography characteristics of ceramic heads was studied with an atomicforce microscope (AFM). Six measurements of the rms and peak-to-valley(pv) roughness parameters were obtained from different AFM images foreach head surface condition. The rails of tested heads and the weartracks on the disks were examined with an optical microscope at highmagnifications. The hardnesses of the modified layers were determined bymeans of a point contact microscope, which is based on the sameprinciple of operation as the AFM. With this technique, nanoindentationswere performed with a three-sided pyramid diamond tip of radius lessthan 100 nm and apex angle of 80 degrees. The diamond tip was mounted ona single leaf spring of stiffness 73 Newtons per meter (N/m). For eachtype of head, six indentations were performed under a fixed load of 66microNewtons (μN). This light load was selected to obtain indentationdepths in the range of 5 to 8 nm in order to minimize the effect of theproperties of the unimplanted bulk material on the hardnessmeasurements. The indented surface topography was imaged in situ withthe same tip at a scan load in the nanoNewton (nN) range. The hardnesswas calculated by dividing the indentation load with the projected areaof the imaged indentation. In the statistical analysis, the roughnessand hardness data were assumed to follow normal distributions.Statistical atomic force microscopy (AFM) data of the rms and pvroughness parameters are listed in Table I. The results show thatsignificant surface smoothening of ceramic heads can be achieved withthe present invention. Surface modification of the heads producedhardnesses slightly higher than that of the original two-phase ceramicmaterial. The mean and standard deviation values of the relativehardness, defined as the hardness ratio of modified-to-unmodified heads,are also listed in Table I. The statistical scatter is attributed to thedifferent hardnesses of the two ceramic phases and the appreciablysmaller size of the nanoindentations relative to the average grain size.Since the hardness depends on both the diamond tip radius andindentation load, it is preferred to consider the relative hardness tocompare quantitatively the mechanical strength resulting from differentmodifications. The results indicate that the present surfacemodification technique enhanced the hardness of the ceramic heads byapproximately 7 to 18%, depending on the type of implanted ions. Itshould be realized, however, that the measured hardnesses are morerepresentative of the subsurface regions where direct and recoilimplantation occurred. Characterization of the near-surface regionswhere film deposition was the principal modification process was notpossible due to surface roughness effects and the extremely small filmthickness (2-3 nm) involved.

                  TABLE I                                                         ______________________________________                                        Roughness parameters and relative                                             hardness of unmodified and modified                                           magnetic recording heads.                                                                Roughness Parameters                                                                           Relative                                          Head      rms (nm)     pv (nm)  Hardness                                      ______________________________________                                        Unmodified                                                                              2.72 ± 0.89                                                                             25.9 ± 4.1                                                                          1.00                                          Ag-modified                                                                             1.98 ± 0.43                                                                             15.8 ± 2.3                                                                          1.07 ± 0.14                                C-modified                                                                              1.82 ± 0.34                                                                             21.4 ± 4.1                                                                          1.18 ± 0.16                                Ti-modified                                                                             1.94 ± 0.51                                                                             16.9 ± 3.0                                                                          1.17 ± 0.17                                ______________________________________                                    

To evaluate the effects of the surface modification technique of thepresent invention on the friction and wear characteristics of magnetichead/disk interfaces, both modified and unmodified heads were rubbedagainst carbon-coated rigid disks. Contact-start-stop (CSS) andcontinuous sliding (drag) experiments were conducted with acomputer-controlled wear tester placed in a class 100 clean-air hood ina laboratory environment with 35-45% relative humidity and ⁻ 27° C.ambient temperature. The tester consisted of a variable speed spindle onwhich the disk was clamped, a lead-screw actuator driven by a step motorfor testing at different radial positions, and a load/friction wirestrain gauge transducer on which the suspension of the head wasattached. To avoid complications associated with wear particlecontamination, a new head and a new disk were used in each experiment. Afixed normal load of about 16 grams(g)(0.1566 N) was used in all the CSSand drag test.

Lubricated thin-film rigid disks with a protective carbon overcoat wereused to conduct the CSS tests. The acceleration, time at maximum speed,and deceleration were chosen to simulate typical disk drive operatingconditions. The velocity versus time profile for CSS testing is shown inFIG. 5. The average values of both friction force and touchdown velocity(TDV) over one revolution were recorded at intervals of 250 cyclesthroughout the tests. The TDV represents the velocity at whichdetectable physical contacts occur as the disk velocity is graduallyreduced. Thus, the TDV was defined as the velocity corresponding to asudden increase in the strain gauge signals. This was accomplished bydecelerating from a velocity of 7.63 m/s at a rate of 0.05 m/s², andsampling the signals from the load and friction force transducers ateach second. Although an abrupt increase in the TDV and the frictionforce can both be considered as failure criteria, the presence of smallamounts of loose wear debris at the interface and material transfer onthe head surface can usually be detected first by the TDV, much earlierthan the formation of a visible wear track on the disk surface. That theTDV exhibits a higher sensitivity to the early stage of wear debrisformation than the friction force was also observed in the CSS tests.Almost all tests were interrupted due to the TDV reaching a setthreshold value of 6 m/s.

Unlubricated carbon-coated disks were used in all the continuous slidingtests. All experiments were performed at a fixed radial distance ofabout 30 mm and a low sliding speed of 3 cm/s, to avoid any runouteffects and lifting of the head due to the establishment of an airbearing film, respectively. The number of sliding revolutions was fixedat 3000. In the first 500 revolutions the friction force was sampled in10-revolution intervals and in the remaining 2500 revolutions in50-revolution intervals.

As shown by FIGS. 6A-6D, the number of CSS cycles to failure isincreased by the surface treatment of the present invention. Thesefigures show the coefficient of friction and TDV versus the number ofCSS cycles for untreated (FIG. 6A) as well as for treated (FIGS. 6B-6D)recording heads. The results from three different experiments for eachsurface modification demonstrate similar trends and consistentbehaviors, except for the TDV at failure where the corresponding numberof CSS cycles exhibits variability. The statistical spread is mostlikely a result of fluctuations in lubrication coverage and thicknessand differences in the disk surface topologies. Failure was assumed tooccur as soon as the TDV reached a value equal to or greater than theassumed failure threshold of 6 m/s. Interfacial failure was alwaysaccompanied with both high friction coefficients and spontaneousincreases in the TDV.

The initial magnitudes of the coefficient of friction and TDV are fairlysimilar, i.e., about 0.16 and 4.5 m/s, respectively, regardless of thehead surface condition. The negligible difference between the initialTDV with modified and unmodified heads indicates that the effect of thesurface modification on the original topography was secondary. In thecase of unmodified heads, FIG. 6A shows that the coefficient of frictionincreased rapidly reaching a maximum of about 0.5 after approximately1750 CSS cycles. At this stage the tests were terminated because the TDVexceeded the threshold value corresponding to failure. Thus for theadopted testing conditions, the number of CSS cycles to failure forunmodified heads is predicted to be less than 2000.

FIG. 6B shows that silver-modified heads exhibited a life to failurehigher by a factor of about two. According to the TDV results, thenumber of CSS cycles for wear debris formation and, hence, interfacialfailure is larger than 2500. The coefficient of friction again increasedat a relatively high rate in the first 500 CSS cycles reaching values inthe range of 0.3 to 0.45.

FIG. 6C demonstrates that the number of CSS cycles to failure ofcarbon-modified heads is larger than 4000. Although the coefficient offriction is similar to that of silver-modified heads, its magnitudeincreased to ⁻ 0.5 slightly before the commencement of failure due towear debris accumulation on the head surface.

FIG. 6D shows that despite the relatively low magnitudes of frictioncoefficients achieved with titanium-modified heads (between 0.3 and0.4), the rapid increase in the TDV indicates that interfacial damageoccurred in less than 2000 CSS cycles, as for unmodified heads.

In view of the results presented in FIGS. 6A-6D, it may be concludedthat, under the CSS testing conditions, the best tribologicalcharacteristics were obtained with carbon-modified heads. The transferof wear debris on the rails of all heads at the stage of failure wasconfirmed with optical microscopy.

Results revealing the evolution of the coefficient of friction with thenumber of sliding revolutions are presented in FIGS. 7A-7D for bothunmodified and modified heads rubbed continuously against unlubricatedcarbon-coated rigid disk. FIG. 7A shows that the coefficient of frictionof unmodified heads increased from an initial value of 0.2 to a markedlyhigher value of about 1.3 in approximately 1000 revolutions. After thisstage, the coefficient of friction exhibited fluctuations which,although on a first sight may appear to indicate erratic frictionbehavior, they can be associated with variations in the real contactarea due to the agglomeration of wear debris. Microscopy studies showedthat a significant decrease in the friction coefficient was always anindication of smearing of wear debris adhering on the head rails.

FIGS. 7B-7D show that significantly better friction characteristics wereobtained with modified ceramic recording heads. Although the initialfriction coefficients were in the range of 0.2 to 0.3, i.e., slightlyhigher than those of unmodified heads, the variability in frictionduring sliding is remarkably small. The best friction behavior wasobtained with silver-modified heads. As shown by FIG. 7B, the frictioncoefficient decreased rapidly for silver-modified heads in the first 200revolutions reaching a steady-state value between 0.1 and 0.2. FIGS. 7Cand 7D show that in the case of carbon- and titanium-modified heads,respectively, the friction coefficient increased very slowly with thenumber of revolutions reaching values in the range of 0.1 to 0.45.Optical microscopy studies showed that the amount of wear debrisobtained with modified heads was much less than that for unmodifiedheads. The lowest wear rates of the disk surfaces resulted from slidingagainst silver-modified heads.

In summary, a cost-effective method for obtaining very smooth, lowfriction, and durable surfaces of magnetic recording heads has beendescribed.

The present invention has been described in terms of a preferredembodiment. The invention, however, is not limited to the embodimentdepicted and described. Rather, the scope of the invention is defined bythe appended claims.

What is claimed is:
 1. A magnetic recording head, comprising:amulti-layer substrate; a thin film layer formed on said multi-layersubstrate; said multi-layer substrate including an intermixed layerincluding a material of said thin film layer intermixed with thesubstrate material and which is formed during ion implantation of thesubstrate material; and said thin film layer formed concomitantly withthe ion implantation of the substrate material.
 2. A magnetic recordinghead, comprising:a multi-layer substrate; a thin film layer formed onsaid multi-layer substrate; said multi-layer substrate including: an ionimplantation layer formed by implantation of ions into a substratematerial, and an intermixed layer including a material of said thin filmlayer intermixed with the substrate material and which is formed duringion implantation of the substrate material, said intermixed layerdisposed between said thin film layer and said ion implantation layer;and said thin film layer formed concomitantly with the ion implantationof the substrate material.
 3. A magnetic recording head comprising:athin film layer deposited on a multi-layer substrate; the multi-layersubstrate including: an intermixed layer forming an uppermost layer ofthe multi-layer substrate, the intermixed layer including a material ofsaid thin film layer intermixed with a material of said substrate, theintermixed layer formed during ion implantation of said multi-layersubstrate due to collisions between ions and the material of said thinfilm layer, said intermixed layer adjacent to said thin film layer; andan ion implantation layer of said multi-layer substrate formed beneathsaid intermixed layer by ion implantation of ions.
 4. The magneticrecording head of claim 3 wherein said multi-layer substrate is ceramic.5. The magnetic recording head of claim 3 wherein said thin film layerincludes silver.
 6. The magnetic recording head of claim 3 wherein saidthin film layer includes carbon.
 7. The magnetic recording head of claim3 wherein said thin film layer includes titanium.
 8. The magneticrecording head of claim 3 wherein said thin film layer has a thicknessin the range of about 2-3 nanometers.